Metabolism and body weight
In simple terms, our*body weight*is a result of catabolism minus anabolism. In other words, the amount of energy we release into our bodies (catabolism) minus the amount of energy our bodies use up (anabolism).
The excess energy is stored either as fat or glycogen (stored as carbohydrate mostly in the liver, and also in the muscles).
One gram of fat produces 9*calories*(kcal), compared to 4 kcal from protein or carbohydrate.
Although becoming overweight is mostly a result of the body storing energy as fat because there is an excess of it, sometimes hormonal problems or an underlying medical condition may affect metabolism.
It is a common belief that slim people have a "high metabolism" while overweight/obese people have a "low metabolism". However, underlying conditions, such as*hypothyroidism*(underactive thyroid) are not the most common causes of*obesity. Weight gain is mainly due to energy imbalance,*according to the UK NHS.4
If you are very overweight or obese it may be advisable to have a medical evaluation to determine whether a medical condition is affecting your weight.
There is not much we can do to significantly change our basal metabolism - our metabolic rate when we are resting. Long-term strategies, such as increasing muscle mass, will eventually have an effect.
However, determining what your body's energy needs are, and then adapting your lifestyle according to that, will have a much faster effect on your bodyweight.
Calorie requirementsBody size and composition*- a larger body mass requires more calories than a smaller body mass does. People with more muscle in relation to fat will require more calories than people who weigh the same but have less muscle in relation to fat. People with a higher muscle-fat ratio have a higher basal metabolic rate than people with a lower muscle-fat ratio who weigh the same.Age*- as we get older several factors emerge which result in lower calorie requirement. Our muscle mass drops, resulting in a higher fat-muscle ratio, our metabolism alters slightly, also resulting in a lower calorie requirement.
The following age-related factors reduce our calorie requirement:Hormones*- Men produce less testosterone and women less*estrogen*with age - both hormones are involved in anabolic processes that consume energy. Human growth hormone, which is involved in anabolism begins to diminish as we age. There is definitely a balance away from anabolic hormones, and towards catabolic hormones as we age - resulting in a much higher susceptibility for high fat-muscle-ratio weight gain.Menopause*- As women approach theirmenopause*there is a drop in hormones which make the body use up more energy. Most women find it harder to lose weight at this time. However, experts say menopausal and post-menopausal weight gain is only partly due to hormonal changes. Other aging factors listed here, such as being less physically active and diet may be the main causes in many cases.Physical activity*- Older people tend to be less physically active than when they were younger. This may not just be due to leisure time lifestyle. A large proportion of young people in physically demanding jobs will have sedentary jobs after the age of 45. This may be because of promotion, the way things are done in some sectors, such as the army, police, fire departments, retraining and entering a new field, or early retirement.Accumulative-waste theory*- As we get older there is a buildup of cells of waste products which probably interfere with metabolism.Gender*- men have a higher basal metabolic rate than women because their muscle-to-fat ratio is higher than women's. This means that an average man will burn more calories than an average woman of the same age and weight.
In simple terms, our*body weight*is a result of catabolism minus anabolism. In other words, the amount of energy we release into our bodies (catabolism) minus the amount of energy our bodies use up (anabolism).
The excess energy is stored either as fat or glycogen (stored as carbohydrate mostly in the liver, and also in the muscles).
One gram of fat produces 9*calories*(kcal), compared to 4 kcal from protein or carbohydrate.
Although becoming overweight is mostly a result of the body storing energy as fat because there is an excess of it, sometimes hormonal problems or an underlying medical condition may affect metabolism.
It is a common belief that slim people have a "high metabolism" while overweight/obese people have a "low metabolism". However, underlying conditions, such as*hypothyroidism*(underactive thyroid) are not the most common causes of*obesity. Weight gain is mainly due to energy imbalance,*according to the UK NHS.4
If you are very overweight or obese it may be advisable to have a medical evaluation to determine whether a medical condition is affecting your weight.
There is not much we can do to significantly change our basal metabolism - our metabolic rate when we are resting. Long-term strategies, such as increasing muscle mass, will eventually have an effect.
However, determining what your body's energy needs are, and then adapting your lifestyle according to that, will have a much faster effect on your bodyweight.
Calorie requirementsBody size and composition*- a larger body mass requires more calories than a smaller body mass does. People with more muscle in relation to fat will require more calories than people who weigh the same but have less muscle in relation to fat. People with a higher muscle-fat ratio have a higher basal metabolic rate than people with a lower muscle-fat ratio who weigh the same.Age*- as we get older several factors emerge which result in lower calorie requirement. Our muscle mass drops, resulting in a higher fat-muscle ratio, our metabolism alters slightly, also resulting in a lower calorie requirement.
The following age-related factors reduce our calorie requirement:Hormones*- Men produce less testosterone and women less*estrogen*with age - both hormones are involved in anabolic processes that consume energy. Human growth hormone, which is involved in anabolism begins to diminish as we age. There is definitely a balance away from anabolic hormones, and towards catabolic hormones as we age - resulting in a much higher susceptibility for high fat-muscle-ratio weight gain.Menopause*- As women approach theirmenopause*there is a drop in hormones which make the body use up more energy. Most women find it harder to lose weight at this time. However, experts say menopausal and post-menopausal weight gain is only partly due to hormonal changes. Other aging factors listed here, such as being less physically active and diet may be the main causes in many cases.Physical activity*- Older people tend to be less physically active than when they were younger. This may not just be due to leisure time lifestyle. A large proportion of young people in physically demanding jobs will have sedentary jobs after the age of 45. This may be because of promotion, the way things are done in some sectors, such as the army, police, fire departments, retraining and entering a new field, or early retirement.Accumulative-waste theory*- As we get older there is a buildup of cells of waste products which probably interfere with metabolism.Gender*- men have a higher basal metabolic rate than women because their muscle-to-fat ratio is higher than women's. This means that an average man will burn more calories than an average woman of the same age and weight.
